The present invention relates to game rackets, and particularly to a racket having a removable stringed inner frame insert.
The construction of rackets for games, particularly tennis rackets, has improved considerably in recent years, with lightweight but very strong materials being used in the construction of racket frames. Tennis rackets are built to be stiffer and are strung more tightly, in order to permit players to impart greater speed to the tennis ball and at the same time control its direction and the amount and direction of spin imparted to the ball. While this tighter stringing permits the desired control and speed to be obtained, one disadvantage is that the shock of impact between the ball and the strings of the racket is generally transmitted through the racket's head and handle to the player's hand and arm. Depending on the material used in the frame and handle of the racket, varying amounts of vibration are transmitted similarly to the player's arm. Such transmission of shock and vibration to the player's hand and arm may be tiring to the player, and may additionally contribute to the injury of the player's wrist, arm, or elbow.
Tennis rackets, particularly when tightly strung, are subject to occasional failure of the strings. Over a period of use the stringing of a racket ordinarily loses some of its tension. In the past, these conditions have required the racket to be restrung. This procedure takes a considerable amount of time and is beyond the skill of most racket users. As a result, restringing usually results in loss of use of the racket for at least a day or more.
Different conditions may make it desirable to use rackets strung with a different amount of string tension. For example, a difference in air temperature may result in a change in the tension in the racket strings. It may therefore be desirable to have rackets strung at different tensions at a given air temperature, in order to have a desired tension at the ambient air temperature where the racket will be used. Different playing surfaces may make it desirable to have more or less tension in the strings of the racket in order to take greater advantage of the ability of the ball to be spun off the playing court surface, or the need to deliver the ball with a great deal of speed where a playing court surface does not permit as effective use of spin.
These problems have been approached previously in several different ways. For example, Shockley, et al, U.S. Pat. No. 3,814,423 discloses a racket having parallel metal frames located on opposite sides of a resilient plastic member which supports the strings of the racket.
Guillem, et al, U.S. Pat. No. 4,206,917 discloses a racket in which the strings are held in tension by passing over a liquid-containing flexible tube in the frame of the racket.
Ryder U.S. Pat. No. 1,558,507 discloses a racket whose head frame may consist of little more than an inflated tube.
Small helical springs have also been embedded in the frames of rackets to provide tension in the racket strings. While these inventions provide for some resiliency in the support of the strings of the racket, when the strings of such rackets break the rackets must still be restrung as in the past.
Li, U.S. Pat. No. 4,185,822 provides a racket having a separate inner frame which holds the pretensioned strings within an outer frame, permitting the inner frame to be replaced by flexibly opening the outer frame. The inner frame of one embodiment of the Li racket is suspended between a pair of pneumatic tubes, but similarly is removable only by flexing open the outer frame of the racket's head.
In another recently developed tennis racket, an outer frame includes a hinge permitting the outer frame to be opened to allow replacement of a stringed inner frame. However, the hinge and outer frame closure of such a racket provide undesirable potential stress concentrations within the outer frame of such a racket, which may cause undesirable flexure patterns in the racket frame or lead to early failure of such an outer frame.
What is needed, then, is an improved sports racket which may be tightly strung yet transmit an acceptably small amount of shock and vibration to the user's arm. Preferably such a racket could be quickly provided with strings having the optimum tension for the playing conditions and could be quickly adjusted to provide a desired amount of stiffness or softness of action of the racket frame.